144 JOURNAL OF THE EOYAL HORTICULTUEAL SOCIETY. 
Humus invariably contains a considerable quantity of nitrogen derived 
from pre- existent combinations in the albuminoids of primitive vegetable 
tissues. Without microbic intervention the researches of M. Hebert have 
demonstrated that these albuminoid matters can play the part of' 
amides ; they can, in fact, give rise to ammoniacal carbonates and 
sulphydrates by simple fixation in water. We find, indeed, the presence 
of these salts in our peat soils, and especially in turfy peat. 
There exists in soils which are rich in humus, and moist, a special 
ferment termed ammoniacal ferment, which appears to act like the 
analogous ferment which in a few days transforms the urates of urine 
into carbonate of ammonia. As the result of numerous experiments, it is 
established now that it is this ammoniacal ferment which commences the 
decomposition of proteic matters : this ferment still retains vitality at a 
temperature of 90° C, which suffices to kill the nitric ferment. 
Fungoid growths intervene also in humid soils in the formation of 
ammoniacal salts ; the bacillus micoides seems also to act in this way. 
The greater part of the nitrogen absorbed by plants in the soil is in the 
form of nitrates.* These nitrates are the result of the successive action in 
the soil of two ferments : the first, the nitromonad, transforms the 
ammonia produced by the ammoniacal ferment into nitrous acid, produ- 
cing consequently soluble nitrites (almost always nitrites of lime). These 
nitrites are extremely unstable, and are rapidly oxidised under the 
influence of another ferment, the micrococcus nitrificans, which then 
produces either nitrate of lime, nitrate of magnesia, or nitrate of 
ammonia. The nitrates are extremely soluble and immediately absorb- 
able by the roots of plants. In order that the nitrification may be rapid 
in a soil, it is essential that a certain number of favourable conditions be ful- 
filled. It is necessary, in the first place, that the circulation of air and of 
water be possible in the soil ; when the soil contains less than 3 per cent, of 
water the nitrification becomes irregular. The intensity of the nitrifica- 
tion varies directly with the quantity of organic matter contained in the 
soil. When, however, a soil contains no lime an excess of organic 
matter retards or hinders the nitrification. In the case, however, of our 
liorticultural soils, very rich in humus, such as leaf-mould and peat-mould, 
nitrification takes place, especially when the water used is slightly 
calcareous. The presence of a certain quantity of lime is of the greatest 
importance, the temperature also plays an important role. Nitrification, 
which attains its maximum at 37° (Centigrade), is almost nil at 5°. The 
pulverisation and frequent working of the soil have the greatest influence 
upon the intensity of the nitrification. To afford an idea of the amount 
of nitrogen placed at the disposal of plants by nitrification in the different 
soils most used in horticulture I give the following examples from my 
own investigations : — 
Loam, or Surrey Turves, total nitrogen .... 4'67 per 1.000 
Nitrification per day and per kilo. . . . 0- 00387 gr. 
Road Sand for Compost Trappes (S Oise), total nitrogen 1-50 per 1,000 
Nitrification per day and per kilo. . . . 0-00029 gr. 
Maurepas Peat Mould (S/Oise), total nitrogen . , 5 per 1,000 
Nitrification per day and per kilo. . . . 0-000199 gr. 
* See "Des formes dans lesquelies I'azote est le plus avantageusement absorbe p.ir- 
les racines des plantes." Paris Horticultural Congress, 1899. 
